get rid of gasoline vapours in waterproof enginehousing

Discussion in 'Boat Design' started by anderswaterjet, Jul 19, 2017.

  1. anderswaterjet
    Joined: Jul 2017
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    anderswaterjet Junior Member

    hello. Im working on a small projekt with my 125 cc suzuki engine. Its watercooled.

    Was wondering about the gasoline vapours and how to get them out.

    The plastic is the engine, the stick is the shaft/rigg , and on it its the fan. Bot inside a closed waterproof box that will proboboly be made in aluminum but not sure yet. The black holes behind the engine is the incomming air so the engine gets oxygen. Will be bigger on real one but this was just a model so. Imgur: The most awesome images on the Internet http://imgur.com/a/yjSYw

    Questions:

    1. will a small fan on the shaft/rigg be enough to get rid of the vapours?
    2. To get the vapours out, how big of a hole is needed and does it matter if its angeld up or down, or striaght? Up: Imgur: The most awesome images on the Internet http://imgur.com/a/Jblvf down: Imgur: The most awesome images on the Internet http://imgur.com/a/1Byh9
     
  2. PAR
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    PAR Yacht Designer/Builder

    Place the engine compartment in negative pressure with fans and some ducting to the bottom of the enclosed area. This causes cool outside air to come into the compartment, and get drawn out the vents. Most commonly you'd place an inline fan (or two) on the top or aft end of the compartment, where the air gets drawn out. The ducts placed low in the compartment, suck off any vapors and get tossed out through the upper vents. If it's an absolutely sealed space, you'll need scuppered intake ports, which would be ideally placed high up on the forward end of the compartment, so cool air goes in, is sucked down to the ducts and out through the fans vents aft.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    A motorbike engine ?
     
  4. anderswaterjet
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    anderswaterjet Junior Member


    thanks, it think u understand, will be making a model and show later. Whats scupperd intake ports? English is not my original languaghe sorry.
     
  5. anderswaterjet
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    anderswaterjet Junior Member

    yes. The reason is i was told i couldnt have an outboard engine i horisontal position otherweise i would have just bought some old 6 hp yamaha or something.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    How does it start ? Electric ?
     
  7. anderswaterjet
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    anderswaterjet Junior Member

    yes
     
  8. messabout
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    messabout Senior Member

    Par has described the conventional method for fuel vapor evacuation. As an addendum: it is important to avoid the use of a fan motor that can make sparks. Many garden variety DC motors do, because they have brushes.
     
  9. Angélique
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    Angélique aka Angel (only by name)

    Merriam Webster Dictionary: scupper

    ‘‘ - - 1) - - an opening cut through the bulwarks of a ship so that water falling on deck may flow overboard
    2) - - an opening in the wall of a building through which water can drain from a floor or flat roof - - - - - - - ’’

    As far as I understand it, "scuppered intake ports" means: Air intake ports with openings in the side walls for the purposes of draining water that gets into the intake ports.

    The scuppers need to be placed as low as possible in the air intake channel, to allow any intake water to flow off the sides, instead of pooling within the sealed engine room.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    If there is any danger of spark from that ( I have no idea, others will likely know), forget it. Not worth the risk.
     
  11. Sparky568
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    Sparky568 Junior Member

    I'm with Mr Efficiency on this one. You are missing some very important basics. The fuel delivery, consumption (carburetor) and ignition systems will need to be marinized to prevent making the front page of your local newspaper or, obituary. Please be safe. :)
     
  12. anderswaterjet
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    anderswaterjet Junior Member

    what if the engine room isnt fully closed? like have a 1x3 inch opening? at least it wouldnt blow up cuz there wouldnt be any preasure when the gas ignite.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Unless you want to look like Wile E Coyote after one of his Acme explosives boxes accidentally detonates, I would not depend on that theory. :)
     

  14. PAR
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    PAR Yacht Designer/Builder

    First of, I should have mentioned (initially) there's no such thing as a truly "watertight" engine compartment. If it was watertight, you'd run out of air for the engine to swallow and it would simply starve. Additionally, it's assumed the blowers are marine inline types that are spark arrested. Anything less is a guarantee you have a big cafriggingboom in your future. This is true of the other elements within any enclosed marine gasoline engine compartment.

    Fuel (gas) doesn't need to be under pressure to invite, just light a match over a bucket of fuel and watch what happens. It does need an open flame and an appropriate fuel/air ratio. A spark is an open flame, just really short in duration, so the same thing. You can isolate the intake air mixture from the compartment and this is a common way to gain a few free horsepower too, but the rest of the system needs to comply (alternators, generators, starters, other electrical devices, etc.). The only way you can have a gas engine in a boat without much fear of a big kaboom, is to leave it completely exposed.
    [​IMG]
    This (above) is a classic example.
    Or if you prefer, one of my designs running up to speed. The engine is fully exposed, though you can only see the headers in this shot.
    SPS-7.jpg
     
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